The present invention relates to a device for the rapid data exchange between two data carriers, more particularly between a fixed station and a movable carrier, by the inductive transmission of logic signals. Such a device is used especially in industrial process automation systems.
For providing inductive transmission of logic signals between a movable data carrier and a fixed reading-writing station, it is known to use:
a resonating circuit connected to an energy source and comprising at least one transmission coil which can be magnetically coupled to a corresponding coil of the data carrier and wound on a high permeability ferrite bar, and a capacitor tuning said circuit to a given frequency; PA1 a circuit for transmitting and a circuit for receiving logic signals, electrically connected to the transmission coil so that this latter has passing therethrough a high frequency current which can be modulated by said signals; PA1 a logic circuit for controlling the exchange, connectable on the one hand to the transmission and reception circuits and on the other to a user system; the resonating circuit may have a single transmission coil operating at transmission and reception or two transmission coils one of which operates at transmission and the other at reception. PA1 an automatic tuning circuit for maintaining the frequency of the resonating circuit at a nominal value and including a comparator means, this means comparing a signal representative of the frequency of the circuit with a reference value and delivering an error signal as a function of their difference; and PA1 a tuning means receiving said error signal and associated with the resonating circuit so as to cause the frequency of this latter to come back to its nominal value.
It has been observed that the presence of metal pieces in the vicinity of the mobile data carrier causes disturbances which risk altering the data exchange between the fixed station and the mobile data carrier. In addition, the dispersion of the values of the components of the transmission circuit, particularly of the capacitors of this circuit, may also cause mistuning of the resonating circuit and consequently the appearance of disturbing signals producing confusion with the useful signals.
Finally, the temperature variations undergone by the device, in particular by the ferrite bar, also risk altering the data exchange.